Effect Of Exogenous H₂O₂on The Seed Germination And Seedlings Physiological And Biochemical Properties In Wheat

Reactive oxygen species （ROS） is a class of substances produced by the metabolism ofplant itself, such as hydrogen peroxide （H₂O₂）, superoxide anion （O2ˉ）, hydroxyl radical（·OH）, singlet oxygen （1O2） and so on. ROS accumulation in response to stress may causeoxidatine damage to cellular components （proteins, membrane lipids, and DNA） and affectthe normal metabolism in plant. Antioxidant enzymes including superoxide dismutase （SOD）,catalase （CAT）, peroxidase （POD）, ascorbate peroxidase （APX） and glutathione reductase（GR） can scanvenge the excessive ROS and relief stress-induced oxidative damage. Inaddition, a increasing number of studies have demonstrated that ROS especial H₂O₂, as asecond messenger, may play an important role in signal transduction in plant responses tobiotic and abiotic stresses. Although, the effect of exogenous H₂O₂on plant physiology andecology has been concerned, the conditions under which be available as a signaling moleculeor be toxic to cells, is still an unresolved question.In the present study, two kinds of wheat which have different drought resistance, cv.Xihan2and Ningchun4, were employed to study the changes of the seed germination andseedling growth, physiological characteristics due to H₂O₂treatment. The main results andconclusions were as follows:（1） Compared to the control, increased germination percentage was observed inNingchun under50and100μmol/L H₂O₂treatments, but different H₂O₂concentrations didnot affect the seed germination of Xihan. In contrast, exposure to exogenous H₂O₂significantly inhibited the growths of roots and shoots in wheat seedlings, and the inhibitoryeffect on roots was more prominent than that on shoots. In addition, the inhibitory effect ofexogenous H₂O₂in Ningchun was more than in Xihan.（2）50,100and200μmol/L H₂O₂resulted in decreased chlorophyll a content, while nosignificant changes in chlorophyll b and total chlorophyll, Fo was observed decreased todifferent H₂O₂concentration, there was an increase of Fv/Fm, Y（Π）, ETR, qP and qL inresponse to different H₂O₂concentration as compared with untreated wheat, and PSâ…¡reaction system more open, and photosynthetic apparatus were damaged more in the minepopulation in Xihan seedlings, but remarkable reductions in Chl a, chlorophyll b and total chlorophyll was observed in Ningchun under different H₂O₂concentration. Fo, Fm, Y （NPQ）,Photochemical quenching （qP and qL）, Nonphotochemical quenching （NPQ and qN）significantly decreased under200μmol/L H₂O₂treatment in comparison with the control.（3） In Ningchun seedlings,50and100μmol/L H₂O₂treatment had induced enhancedSOD activity; the inhibit of CAT were observed, but the excitaction of GR in response to only200μmol/L H₂O₂treatments, significant enhancement in APX activity was showed underdifferent H₂O₂concentrations. Additionally,50,100and200μmol/L H₂O₂treatmentsdecreased H₂O₂and MDA contents, and induced the increase of APX, CAT and GR activitiesin Xihan. No significant changes in POD activity was found in two cultivar leaves of wheatseedlings under exogenous H₂O₂treatment.（4） The elevated levels of soluble sugar and proline were observed in Xihan exposed toexogenous H₂O₂, while H₂O₂treatment induced significant decrease in soluble sugar contentin Ningchun, and there was a proline accumulation in response to only200μmol/L H₂O₂treatments. No significant change in soluble protein content was exhibited in two kinds ofwheat treated by H₂O₂. In Xihan seedlings, OAT activity decreased by78%and83%of thecontrol value under50and100μmol/L H₂O₂treatment, respectively;200μmol/L H₂O₂led toabout16%elevation in PDH activity.In conclusion, our results suggested that chlorophyll content destroyed but that activitiesof antioxidant enzymes enhanced in wheat seedlings under H₂O₂stresses, thus the strongereffects of antioxidanted role was existed and enhanced wheat seedlings tolerance to H₂O₂stress. Therefore there was no significant change in MDA content between the control andH₂O₂-treated wheat seedlings. And significant accumulation of soluble sugar and praline dueto exogenous H₂O₂was found in Xihan seedlings in comparison with Ningchun seedlings,which indicated that Xihan was more tolerance to oxidative stress; and also, the elevation ofproline content was associated with slight change in PDH activity in Xihan seedlings, andwith significant increased OAT activity in Ningchun seedlings under H₂O₂treatment.